The extracellular acid protease produced by Rhizopus chinensis contains at least three different isoelectric forms. The amino acid sequence of the pI 5.15 form will be determined and a comparative study of the other isoelectric forms made to detect the differences in their structures. This information will be utilized to confirm or correct the tertiary structure solution by X ray diffraction performed by others. Contributions of various amino acid functional groups to the mechanism of action are being investigated.